Ciprofloxacin distribution was assessed in cerebral tissues in 14 patients undergoing craniotomy. The study objective was to determine the brain tissue/serum concentration ratio of ciprofloxacin. Patients received a single intravenous (iv) 200 mg dose of ciprofloxacin. Mean (+/- S.D.) tissue/serum concentration ratios were (mg/kg): parietal fat during opening 1.40 +/- 1.05, during closure 1.34 +/- 1.17, in the dura mater 2.26 +/- 1.36, in skull bone during opening 0.44 +/- 0.29, during closure 0.97 +/- 1.57 and in brain tissue 0.88 +/- 0.99. Mean (+/- S.D.) concentrations of ciprofloxacin in brain tissue were 0.87 +/- 0.08 mg/kg, suggesting that a dose >200 mg iv ciprofloxacin is required to ensure therapeutic concentrations in brain tissue.